In recent years, the development of ceramic matrix composites (CMC) as one type of fiber-reinforced composite material is being promoted. CMC is a composite material in which ceramic fiber is reinforced with a matrix, and is characterized in being light and having superior heat resistance properties. By leveraging these characteristics, for instance, the possibility of using CMC in aircraft engine parts is being considered, and the practical application thereof is currently being sought. Note that the use of CMC as aircraft engine parts is expected to considerably improve the fuel economy.
The general process of forming CMC is as follows. Foremost, roughly several hundred ceramic fibers are bundled to prepare a fiber bundle, and the prepared fiber bundles are woven into a fabric. As the weaving method of fiber bundles, for instance, known are methods referred to as three-dimensional weaving and plain weaving. Three-dimensional weaving is a method of weaving the fiber bundles from three directions (XYZ directions) to prepare a fabric, and plain weaving is a method of weaving the fiber bundles from two directions (XY directions) to prepare a fabric.
After the fabric is prepared, a matrix is formed in the voids in the fiber bundles and between the fiber bundles via matrix forming processes known as CVI (Chemical Vapor Infiltration) and PIP (Polymer Impregnation and Pyrolysis). The CMC is thereafter formed by ultimately performing machining and surface coating.
Here, while CVI and PIP in the formation process of CMC are processes for forming a matrix in the voids, in effect it is difficult to form a matrix for filling all voids. Thus, a matrix is not formed and voids will remain on the surface and inside the formed CMC. The distribution of these remaining voids will considerably affect the strength of the CMC.
For example, in cases where numerous voids exist in a local area, the strength of that local area will deteriorate considerably. Thus, in order to confirm whether the strength of the formed CMC is constant or sufficient, it is important to appropriately evaluate the void distribution. In other words, it is important to accurately extract the voids.
PTL 1 discloses a technique of creating a void extraction image from an X-ray transfer image of an engine skirt. Specifically, morphology processing is executed to the X-ray transfer image of the engine skirt for eliminating noise, binarization processing is executed to the image that underwent the morphology processing, and a circular foreground in the image that underwent the binarization processing is determined to be a void and extracted. Meanwhile, with regard to an oval foreground in the image that underwent the binarization processing, a circular foreground within the oval shape is extracted by once again executing binarization processing upon changing the threshold, and this is determined to be a void and extracted. Finally, a void extraction image is created by synthesizing the plurality of circular voids that were extracted.